Process for manufacturing improved refractory brick



Oct. 4, 1966 E. P. WEAVER 3,

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INVENTOR,

ERNEST P. WEAVER RUPTURE AFTER COKlNG IN SERVICE WWW ATTORNEY United States Patent 3,276,889 PROCESS FOR MANUFACTURING IMPROVED REFRACTORY BRICK Ernest P. Weaver, Pittsburgh, Pa., assignor to Harbison- Walker Refractories Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 8, 1965, Ser. No. 446,628 4 Claims. (Cl. 106-281) application Serial No. 220,132, filed August 29, 1962,

entitled Refractory Practices, now abandoned.

In a particular embodiment, this invention relates to a method of providing tar bonded refractory shapes having increased green density and increased strength after exposure to elevated service temperatures.

The principal refractory materials used in lining oxygen steelmaking vessels include dead burned magnesite or magnesia (MgO), dead burned dolomite (MgO-CaO), hard burned lime (CaO), and mixtures thereof. Conventionally, the foregoing are bonded with pitch for better service life. Better service life with this type of refractory appears to be directly related to the strength of the brick after being subjected to elevated coking temperatures. In actual service, there is a temperature gradient throughout the length of the brick in the working lining of the steelmaking vessel. Since the strength of the brick is related to the coking temperature, there is also variation in strength through the brick. It is, therefore necessary ,to have superior strength after any coking temperature above approximately 500 F.

It is a primary object of thisinvention to provide tar bonded, basic refractory shapes having increased green density-and increased strength after exposure to elevated temperatures, as compared with the previously available tar bonded refractories of this type. It is another object of this invention to provide shapes containing at least one material of the group, dead burned magnesia, dead burned dolomite, and hard burned lime, bonded with a mixture strength at elevated temperatures may be had in basic refractory shapes bonded with a mixture of liquid tar and powdered pitch when at least a portion of the pitch is coball milled with a major portion of the fine fraction of the refractory batch (at least about 90% of the fines and 50% of the pitch is a workable ratio), with the remainder of the pitch being added at the mixer with the remainder of the batch and the liquid tar. This batch is then shaped by pressing at about 8000 p.s.i.

The drawing shows the approximate temperature gradient and strength after coking changes throughout a tar bonded brick in the working lining of a basic oxygen furnace. The temperature gradient is represented by line A. The temperature at any point between the hot face and the working lining-tank lining interface is determined by drawing a vertical line to intersect line A and then a line horizontalfrom that intersection to the scale on the left.

The hot face temperature of the Working lining is about 3000 F. in vessels used for oxygen steelmaking. The

working lining-tank lining interface is about 500 F.

Line B represents the changing modulus of rupture after coking of prior art brick as a result .of the temperature gradient. Line C represents the changing modulus of rupture after coking .of the improved brick of this invention. As explained above, the strength after coking at any point in the brick is determined by drawing a vertical line until it intersects lines B or C and then a horizontal line from that intersection to the scale on the right. 5 Uncoked strengths are shown in the drawing at D and E.

Considering the drawing, it is apparent that while tar bonded brick manufactured according to this invention have lower strength before coking than certain products of the prior art, it has much higher strength after coking in service where the strength is needed most.

This invention relates to the manufacture of tar bonded refractories using the double pitch bond taught in US. Patent 3,070,449 of the same assignee. In that patent it was taught that higher residual carbon content can be obtained in brick of this type by using two different pitches for bonding purposes and including one pitch in the batch as a fine powder.

In the general art to which this invention relates, commercially available tars and/or pitches are divided into three categories. The first is soft pitch or tar, which has a softening point within the range of about 80 to 100 F.; the second softens within the range of 150 to 250 F., and hardens upon cooling; and the third pitch is known as hard pitch, which has a softening point of 275 to 350 F. The second is usually liquified by heating and usedfor brick bonding purposes. The third can be ground to a powder and handled at room temperature (about 70 F.) as a powder without promptly coalescing. As to the powdered pitch discussed below, while the separate powder particles may vary, it is preferable to have all pass a 100 mesh Tyler screen.

In addition to the characteristics above noted, for this invention, it is necessary that the tar and pitch materials be nonaqueous and cokable.

The advantages of the invention can be obtained in refractory shapes of almost any basic refractory material or mixture thereof, and including such materials as dolomite, lime, magnesia, etc, and mixtures thereof. Further, it is preferable that the dolomite, lime and magnesia constituents be in a dead burned state. In the following discussion, when liquid bonding pitch is mentioned, this refers to a heated tar or pitch, Which is maintained at a temperature about 100 F. above its softening point, or such other temperature as imparts fluidity to the material.

The invention will be further described in conjunction with the following specific examples, in which detailed explanation is given by way of illustration and not by way V of limitation. In all of the following examples, a refractory batch composition was formed of about 60%, by weight, of a pre-burned refractory clinker and about 40% of dead burned magnesite (magnesia). The clinker and magnesite had the following typical chemical analysis:

Table I Clinker, Percent Dead Burned Magnesite, Percent 9. 0 3. 5 23. 0 0. 9 59. 5 94. 9 4. 5 0. 3 Alumina (A120 l. 5 0. 4 Chromic Oxide (CI'203) 2. 5 0. 0

. 3 burning more or less as equivalents, since the act of burning the brick serves to coke the pitch ingredients.

All of the examples were made-with 2%, by weight, powdered pitch and 5% liquid pitch, as shown in Tables II and III.

Example I was prepared by first heating the liquid bonding pitch to about 100 F. above its softening point (the temperature which imparted fluidity to the bonds). Then a portion of the aggregate, the coarser portion, was incorporated in the liquefied pitch. The coarse fraction was also heated, so quenching of the pitch did not occur. Thereafter, the remainder of refractory batch was added. Finally, the powdered pitch was blended into the batch. This batch was prepared according to the teachings of United States Patent No. 3,070,449.

Example II was prepared in a manner similar to Example I, except that l% of the powdered pitch was co-ball milled with the magnesite fines. The other 1% powdered pitch was blended into the batch as in Example I. Example II is the preferred embodiment of this invention.

Table II.-Efiect f co-ball milling magnesite and powdered pitch Base mix: Percent Clinker 60 Magnesite ball mill fines 40 Liquid bonding pitch Powdered pitch 2 Example No I II Method of Adding Pitch Bulk Density, p.c.f.:

Before Burn 179 180 After 2,000 F. Burn 172 173 After 2,730 F. Burn 170 171 Modulus of Rupture, p.s

Before Burn 1, 700 920 After 500 F. Burn 1, 300 1, 500 After 2,000 F. Burn- 360 490 After 2,730 F. Burn 590 730 l 2% Added At Mixer. 2 1% 00-13211 Milled and 1% Added At Mixer.

Table H, including Examples I and H, establishes that the manner of adding the powdered pitch is critical. When at least a portion of the pitch is co-ball milled with a major portion of the fine fraction of a refractory batch, with the rest of the pitch being added at the mixer with the remainder of the batch and the liquid tar, the strength after coking at elevated temperatures and, also, bulk density are increased. The green strength is not, however, increased. The green strength is only necessary in shipping and handling the brick prior to service. The green strength of Example II is adequate.

Brick made according to this invention (Example H) are stronger after coking at all temperatures than brick of the prior art (Example I).

The strength after coking varies somewhat from test to test. Table HI includes a retest of Examples I and II,

. plus Example III, in which all the powdered pitch was co-ball milled.

Table III Example No I 1 II 1 III Method of Adding Pitch Bulk Density, p.c.f.:

Before Burn 180 After 2,730 F. Burn 170 Modulus of Rupture, p.s.i. After 2,730 Burn. 990

1 Retest.

2 2% Added At Mixer.

3 1% (Jo-Ball Milled And 1% Added At Mixer. 4 2% C0-Ball Milled.

4 magnesite fines was stronger, after burning or coking. This is not to say there is an optimum coking treatment not disclosed. In actual service, brick are coked in place. Burn-in procedures (in situ coking) vary from furnace to furnace, and even within the same furnace.

Table II establishes that all of the powdered pitch should not be co-ball milled. Example III, following this procedure, has poorer strength after coking than Example H made according to the teachings of this invention.

Having thus described the invention in detail and with sufficient particularly as to enable those skilled in the art to practice it, what is desired to have protected by Letters Patent is set forth in the following claims.

I claim:

1. In a process for the manufacture of refractory brick from a size graded basic refractory material, said refractory material selected from the group consisting of dolomite, line, magnesia, and mixtures thereof, in which about 5070% is a coarser fraction which rests on a.65 mesh screen and about 50-30% is a fines fraction which passes a 65 mesh screen, and about 5%, by weight, based on the total weight of the refractory, of bonding pitch having a softening point in the range .150 to 250 F., and about 2%, by weight, based on the total weight of the refractory of powdered pitch passing a 100 mesh screen and having a softening point above about 275 F., the improvement which comprises co-ball milling about 50% of the powdered pitch with about of the fines fraction of the refractory before mixing with the other ingredients of the batch.

2. In a process for the manufacture of refractory brick from a size graded basic refractory material in which about 5070% is in a coarser fraction which rests on a 65 mesh screen and about 5030% is in a fines fraction which passes a 65 mesh screen,-and about 5 by weight, based on the total weight of the size graded basic refractory, of bonding pitch having a softening point'in the range 150-250 F., and about,2%,, by weight, based on the total weightof the basic refractory of powdered pitch which passes a mesh screen, said powdered pitch having a softening point above about 275 F., the improvement which comprises co-ball milling about 50% of the powdered pitch with about 90% of the fines fraction of th refractory batch before mixing with the other ingredients of the batch. I

3. In a process for manufacturing tar bonded basic refractory shapes manufactured from basic refractory batches, said batches being made in a known manner of a mixture of size graded basic refractory materials of which about 50-70% is a coarser fraction which rests on a .65 mesh screen and in which about 50 to 30% is a fines fraction which passes a 65 mesh screen, and in which the tar bonding material is a mixture of ,nonaqueous cokable carbonaceous bonding materials selected from the artrecognized groups: pitch having a melting point between about and 250 F., and 100 mesh powdered pitch which has a softening point above about 275 F., the improvement whichcomprises co-ball milling about 50% of powdered pitch with about 90% of the fines fraction of the refractory batch.

4. A process according to claim'3, in which said fines fraction being substantially entirely magnesia.

References Cited by theExaminer UNITED STATES PATENTS 540,465 6/1895 Talbot 106-58 569,859 10/1896 Cotter et a1 106'280 3,070,449 12/ 1962 Davies et a1. l06-281 FOREIGN PATENTS Y 775,087 5/ 1957 Great Britain.

ALEXANDER H; BRODMERKEL, Primary Examiner.

J. B. EVANS, Assistant Examiner. 

1. IN A PROCESS FOR THE MANUFACTURE OF REFRACTORY BRICK FROM A SIZE GRADED BASIC REFRACTORY MATERIAL, SAID REFRACTORY MATERIAL SELECTED FROM THE GROUP CONSISTING OF DOLOMITE, LINE, MAGNESIA, AND MIXTURES THEREOF, IN WHICH ABOUT 50-70% IS A COARSER FRACTON WHICH RESTS ON A 65 MESH SCREEN AND ABOUT 50-70% IS A FINES FRACTION WHICH PASSES A 65 MESH SCREEN, AND ABOUT 5%, BY WEIGHT, BASED ON THE TOTAL WEIGHT OF THE REFRACTORY, OF BONDING PITCH HAVING A SOFTENING POINT IN THE RANGE 150 TO 250*F., AND ABOUT 2%, BY WEIGHT, BASED ON THE TOTAL WEIGHT OF THE REFRACTORY OF POWDERED PITCH PASSING A 100 MESH SCREEN AND HAVING A SOFTENING POINT ABOVE ABOUT 275*F., THE IMPROVEMENT WHICH COMPRISES CO-BALL MILLING ABOUT 50% OF THE POWDERED PITCH WITH ABOUT 90% OF THE FINES FRACTION OF THE REFRACTORY BEFORE MIXING WITH THE OTHER INGREDIENTS OF THE BATCH. 